The present invention refers to a device for folding flaps of box blanks having crease lines transverse to the travelling direction of the blanks, for use in a folder-gluer. The device comprises a rotary member rotatable around an axis transverse to the travelling direction, provided with at least one folding member.
Devices for folding flaps of folding boxes with a folding member mounted on a transverse rotary shaft and comprising a single folder in the shape of a hook are well known. Another well known similar device comprises two hook-shaped folders which are symmetrically arranged with respect to the axis of the transverse rotary shaft. This or these folders are mounted on a central hub which is laterally movable along the transverse rotary shaft. The box blank travels above the rotary folding member and the folders will fold the flap from the rear while the box blank is travelling. Consequently, the folder should move at a higher speed than the box blank.
In order to fold the flap, the end of the folding hook must contact the flap to be folded in a favorable area situated at about two thirds of the flap length taken from the transverse crease line around which the flap must be folded. The transverse shaft of the rotary folding member is situated at a given distance from the passage plane of the blanks and, in order to work in the favorable area of the flap to be folded, it is necessary to either adapt the length of the hooks or to position shims on the central hub supporting the folding hooks. A device of this kind is described in U.S. Pat. No. 3,330,185. The main drawback of this device is the adjustment time required and the difficulty of positioning the folding hook in the favorable folding area.
To obviate the drawbacks of the aforesaid solution, FR 2,597,027 describes a device wherein a plurality of motors are controlled by a pulse converter that converts the values of the movement curves calculated by a function generator receiving data from a detector of passage of the blanks and the settings relating to the characteristic dimensions of these blanks. Each of these various motors acts according to different degrees of mobility of the device, and the motors allow optimizing the movement of the folding hooks.
However, such a solution is relatively complex and hence expensive. This complexity is mostly due to the fact that the folding device occupies a determined position on the folder-gluer, whereas the dimensions of the cardboard blanks may substantially vary. Also possible are blanks having transversely aligned flaps to be folded which are of different lengths. This implies to provide two devices on a common transverse support which are adjusted according to the respective lengths of the flaps.